1. Field of the Invention
The present invention relates to a cooling system for a jet propulsion boat wherein a jet of water for propelling the boat is emitted by driving a jet propulsion unit with an engine. In particular, a part of the jet of water from the jet propulsion unit is utilized for cooling the engine.
2. Description of Background Art
A jet propulsion boat is a vessel provided with a jet propulsion unit mounted at a rear portion of the vessel body. The jet propulsion boat is propelled by sucking water from the vessel bottom by driving the jet propulsion unit by the engine. The sucked water is then emitted rearward as a jet of water. Such a jet propulsion boat is provided with a cooling system for cooling the engine or the exhaust system while being propelled.
A cooling system for a jet propulsion boat is known from, for example, JP-A-10-238358 entitled “FOUR-CYCLE ENGINE AND SMALL PLANING BOAT HAVING THE SAME.” The contents of the above publication are illustrated in FIG. 13 of the present invention and the cooling system of the jet propulsion boat will be described below.
FIG. 13 is a general view showing a principal portion of the cooling system for a jet propulsion boat according to the background art. The jet propulsion boat 150 is provided with an engine-cooling flow path 152 for cooling the engine 151. The engine-cooling flow path 152 includes an inlet path 153 through which a part of the jet of water is taken as cooling water. The inlet path 153 is connected to the engine-cooling duct (for example, a jacket water). The engine-cooling duct is provided with a thermostat valve 155 and a relief valve 156 at the rear end portion 154 thereof. The engine-cooling duct is further provided with a constantly opened drainage duct 157 and a relief drainage duct 158 at the rear end portion thereof.
The engine-cooling flow path 152 is a flow path constructed in such a manner that a part of the jet of water emitted from the jet propulsion unit 160 is taken as cooling water by facing the inlet port 153a of the inlet path 153 toward the interior of the jet propulsion unit 160. Cooling water taken therein is introduced into the engine-cooling duct. Furthermore, the cooling water introduced into the engine-cooling duct is discharged from the constantly opened drainage duct 157 as shown by the arrow a.
According to the jet propulsion boat 150, the jet propulsion boat 150 is propelled by driving the engine 151 and thereby rotating blades 161 of the jet propulsion unit 160, and emitting a jet of water from the steering nozzle 162.
In this case, a part of the jet of water emitted by the jet propulsion unit 160 is taken through the inlet port 153a of the inlet path 153 as cooling water. The cooling water taken therethrough is introduced into the engine-cooling duct. Furthermore, the engine 151 is then cooled by the cooling water thus introduced. After the engine 151 is cooled, the cooling water is discharged from the constantly opened drainage duct 157 toward the outside as shown by the arrow a.
When the temperature of the cooling water exceeds a threshold value while cooling the engine 151, the thermostat valve 155 opens and discharges the cooling water through the relief drainage duct 158 as shown by the arrow b. Accordingly, the cooling water flowing in the engine-cooling flow path 152 is kept at a preferable temperature.
When the hydraulic pressure of the cooling water exceeds a threshold value, a relief valve 156 opens and discharges the cooling water through the relief drainage duct 157 as shown by the arrow b. Accordingly, the cooling water flowing in the engine-cooling flow path 152 is kept at a preferable hydraulic pressure.
In this way, providing the thermostat valve 155 and the relief valve 156 in the engine-cooling flow path 152 enables to cool the engine 151 while maintaining cooling water in the preferable state in terms of temperature and hydraulic pressure.
However, the engine-cooling system of the jet propulsion boat 150 in the background art requires the thermostat valve 155 and the relief valve 156 for maintaining the temperature and the hydraulic pressure of the cooling water in the preferable state. In addition, the background art requires two drainage ducts including the constantly opened drainage duct 157 and the relief drainage duct 158 for draining the cooling water. Therefore, the number of components of the engine-cooling flow path 152 increases, which hinders reduction of the cost. Furthermore, increasing the number of components makes the structure complex, and thus it takes time for assembling the engine-cooling system of the jet propulsion boat 150, which hinders increase an in productivity.